We turn to that rescue in a Utah canyon where a father and his two young sons were stranded for three days surviving with a single granola bar and precious little water. John muller has his story. Reporter: This morning a dramatic story of survival Jason thought he might never live to tell. Anything could have happened. Reporter: Jason knight and his two sons, 8 and 11, rescued after a nearly four-day ordeal in the santhrax canyon with barely any food or water. He planned to take them to a far less dangerous canyon when he took a wrong turn. It was supposed to be a three-hour tour. Everything out there looks the same. Reporter: He then formed a plan telling his boys to stay put on a safe ledge while he continued down to find an escape. That's when things went from bad to worse with knight finding himself trapped in the narrow walls of the canyon. 350 feet down from his children. They could not hear me. I could not hear them. Reporter: Knight waited and worried for a gut-wrenching three days. Finally a break when knight and the boys failed to return home on schedule Friday. Knight's wife alerted county officials who launched a massive search. Incredibly a helicopter was able to locate the boys. It turns out they'd survived off a small amount of water and a single granola bar. So I put them in a place where the helicopter could easily find them. I knew that if something bad happened to me if they found them they could probably find me. Reporter: And find them he did just a half hour later. Incredibly they escaped with only bumps and bruises. We were in a bad situation and without preparedness and without the rescue people, we wouldn't have made it out. Reporter: For "Good morning America," John muller, ABC news, New York.

This transcript has been automatically generated and may not be 100% accurate.

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